Response of size-fractionated phytoplankton to environmental factors near the Changjiang Estuary

Size-based partitioning of phytoplankton is a useful tool for monitoring key phytoplankton traits, and it provides a better understanding of phytoplankton dynamics. Our aim is to determine the variation in the different size classes of phytoplankton to the total phytoplankton biomass during the spring and autumn of 2010 and examine the relationship between phytoplankton size structure and environmental variables and zooplankton community structure near the Changjiang Estuary. In the spring, phytoplankton populations were predominantly consisted of nanophytoplankton throughout the study region. In the autumn, picophytoplankton and nanophytoplankton collectively dominated the phytoplankton community. A Pearson correlation analysis highlighted the role of temperature and trophic conditions on the contributions of nanophytoplankton and picophytoplankton. The grazing pressure exerted by mesozooplankton could have played an important role in determining the microphytoplankton community structure.

Morphology and molecular phylogeny of three species of Coolia(Dinophyceae)from Hainan Island,South China Sea

Marine benthic dinoflagellates in the genus Coolia were reported in both tropical and temperate regions.We conducted a morphological and phylogenetic characterization of Coolia species from Hainan Island,South China Sea.The morphologies of three Coolia species were similar to those of the original descriptions of Coolia canariensis,C.tropicalis,and C.malayensis.In phylogenetic analyses based on the LSU rDNA and ITS regions(ITS1-5.8 S-ITS2),the Hainan strains of C.canariensis,C.tropicalis,and C.malayensis clustered within the clades of these species with other isolates from different areas.No differences(p-distance)in LSU rDNA sequences were found between the Hainan C.malayensis strains and the strains from New Zealand,Florida of USA,Malaysia,Japan,Dominican Republic and Guangxi and Hong Kong of China.For C.canariensis and C.tropicalis,no differences(p-distance)in the LSU rDNA sequences were found between the Hainan strains(D1 C2 and DS5 F4,respectively)and the Australian strains(NQAIF252 and NQAIF90,respectively).Our study reveals the morphological and genetic diversity of Coolia species from Hainan Island,South China Sea,which provides a detailed understanding of Coolia species of this area.

Karlodinium elegans sp. nov. (Gymnodiniales, Dinophyceae), a novel species isolated from the East China Sea in a dinofl agellate bloom

Abstract On May 24–29,2019,a harmful algal bloom occurred in Pingtan coastal areas,Fujian,southeast China,and caused mass mortality of cage-cultured fi sh.Two clonal cultures of an unknown naked dinofl agellate were set up from seawater samples taken during the bloom.The cultures were examined for morphological features,ultrastructure characters,photosynthetic pigments,the large subunit(LSU)of the rRNA gene,and the internal transcribed spacer(ITS)sequences,as well as acute toxicity analysis.The cell was unarmored,small-sized,and ovoid,and was characterized by elaborate striations on the epicone and hypocone.The nucleus was large,ellipsoid to oval or kidney-shaped,and centrally located in the cell.A long linear apical groove originated above the sulcus in the ventral epicone and extended to the dorsal side.An elongate,slit-like“ventral pore”was located on the left of the epicone,well away from the apical groove.The chloroplasts were yellowish brown,numerous,band like,and irregularly distributed in the cell periphery.Fucoxanthin was the main accessory pigment composition.Phylogeny topology reconstructed on partial LSU rDNA showed that the unknown dinofl agellate branched as a sister species to Karlodinium sp.(strain IFR981&IFR797,from France)and Karlodinium corrugatum(strain KDGSO08,from Australia),with genetic divergences of 0.6%and 3.3%,respectively.Based on the morphological and molecular phylogenetic analysis,we describe the novel dinofl agellate as Karlodinium elegans sp.nov.A toxicity assay revealed that the clonal culture of K.elegans(strain PTB601)had no adverse eff ect on brine shrimp(Artemia salina)and marine medaka(Oryzias melastigma),indicating it may not be a toxic species.

Is the dinoflagellate Takayama xiamenensis a synonym of Takayama acrotrocha (Kareniaceae, Dinophyceae)?

The naked dinoflagellate Takayama acrotrocha was identified as responsible for a bloom in Shenzhen Bay,Guangdong,China,in early spring 2021.The identification was confirmed by light,scanning,and transmission electron microscopy and molecular data based on the LSU ribosomal DNA(rDNA)and ITS rDNA sequences.This is the first record of T.acrotrocha bloom in the South China Sea.The sulcus of T.acrotrocha was wide and extended onto the epicone as a short intrusion in general,sometime the intrusion was not apparent and some were finger-like.The apical groove was deeply sigmoid.The nucleus was large,ovoid to cup-shaped and occupied most of the epicone.A large,rounded pyrenoid surrounded by a starch sheath was located at the left side to the centre of the hypocone.Under epifluorescence illumination,a row of large vesicular knobs was observed on the upper border of the cingulum.The intraspecific morphological variabilities in the clonal cultures of T.acrotrocha were investigated carefully.Cells that share the same diagnostic characters used for the description of Takayama xiamenensis such as the finger-like sulcus,a large nucleus located in the epicone and the similar pyrenoid type were observed.The LSU rDNA sequences of T.acrotrocha and T.xiamenensis only differed in 3 base pairs(bp)for a sequence length of 673 bp(with a similarity of 99.55%).For these reasons,we propose T.xiamenensis as a junior synonym of T.acrotrocha.